Without limiting the scope of the invention, its background is described in connection with existing self-propelled modular transporters (“SPMT”) for transport of very heavy and large loads weighing tens to hundreds of tons. SPMTs are a combination of a trailer unit and a power pack unit (“PPU”). In simplest form, the trailer unit includes two longitudinal rows of paired wheels such that viewed from the top there would be 4 longitudinal lines of wheels, two on one side and two on the other side. Each wheel pair has its own axle. Viewed from the side, there will typically there will be 3, 4, 5, 6 or 8 axle assemblies visible representing half of each cross-wise matching set for a total of (respectively) 12, 16, 20, 24 or 32 wheels per module depending on the number of axle assemblies. Each axle of a given wheel pair can swivel independently of the other wheel pairs and some or all of the wheels are individually controlled and hydraulically propelled. Each wheel assembly communicates with a controller that commands the wheel assembly to turn, brake or rotate. Electronic control of the wheel assemblies allows for synchronous steering with unitary control of the wheel assemblies. The wheel assemblies can also be raised and lowered hydraulically to adjust the vertical height of the deck and can move up and down independently to allow movement over uneven surfaces without up and down movement of the upper load carrying deck.
Typically, SPMTs are constructed with a single deck having two longitudinal lines of wheel pairs mounted underneath. Such an arrangement would be considered a double axle trailer or one line. Alternatively, a given longitudinal string of single axle wheel pairs may have its own deck such that in use two long single axle wheel-pair trailers would be bolted together to form a unitary deck. Because the trailers are modular, they are strung together end-to-end to increase the overall length of the combined modules.
Typically, when widthwise extension of the trailer platform is required for very wide loads, a series of trailers will be run together side-by-side as shown in FIG. 1B. Flexibility of the width of combined trailers has been obtained with combinations such as for example a triple axle arrangement with a double axle trailer combined with a single axle trailer to form three longitudinal lines of wheel pair assemblies with 6 wheels across in three pairs.
However, such a parallel arrangement consumes a large number of trailers. More recently, split trailers have been developed in which two single axle wheel-pair trailers are separated by telescopic bars that connect the trailers. Problematically, the telescopic bars prevent the two trailers from coming close together and/or project from the sides of the trailers.
Provided herein are novel extension mechanisms to provide variable extension widths of SPMT trailers while providing the required stability of a unitary structure.